A first type of pulley is the sheave which allows a rope to be redirected when it passes through the central recess of the sheave (a pulley wheel having a groove).
Those low-friction sheaves provide a relationship of solidity/weight/price in all cases because there is no component in rotation. The resistance to friction is obtained only by the fiber of the rope to be redirected and the fiber which is used to fix the sheave. That product is increasingly present on ocean racing boats because it is a guarantee of reliability. The major disadvantage thereof is that it greatly increases the occurrences of friction of the rope which passes at the center thereof, and consequently it is necessary to have a great deal more energy in order to maneuver the rope than on a conventional pulley.
A second type of pulley comprises a ball bearing sheave, that is to say, a pulley with a sheave which rotates by means of a ball bearing. That ball bearing sheave provides a very small friction coefficient. That type of pulley is very efficient and allows the production of complex force step-down systems. The disadvantage of those pulleys is that they are expensive when they are provided for heavy loads. They also require maintenance and regular inspection owing to the presence of the ball bearing. Another disadvantage is that, if the axis, the lateral faces or the engagement location should break, then the connection will be broken between the rope and the engagement location and collateral damage will be brought about for the system as a whole. Furthermore, the performance of the ball-type pulleys which are configured for heavy loads are also heavy. For example, in the nautical field, that disadvantage is detrimental to the performance of a boat.
An object of the present invention is to overcome those disadvantages and to provide an improved pulley which reduces the occurrences of friction on the rope to be redirected whilst having a great load-bearing capacity, for a reduced weight.